A high-pressure turbine of a turbomachine comprises at least one stage comprising an upstream guide vane element formed of an annular array of fixed stator blades and an impeller mounted so as to rotate downstream of the upstream guide vane element in a cylindrical or frustoconical assembly of ring sectors placed circumferentially end-to-end. These ring sectors comprise, at their upstream and downstream ends, means for coupling to an annular support that is attached to an outer casing of the turbine by suspension means.
The radial clearances between the movable blades of the impeller and the ring sectors must be minimized to improve the performance of the turbomachine while preventing friction of the ends of the blades on the ring sectors, which would cause these ends to wear and the performance of the turbomachine to deteriorate at all operating speeds.
The upstream guide vane element of the high-pressure turbine comprises two coaxial walls of revolution which extend one inside the other and which are connected together by the fixed stator blades. It is fitted into the turbomachine by its inner wall of revolution which comprises an annular flange for attachment to an inner casing of the turbine. Sealing means are also provided at the upstream and downstream ends of the walls of revolution of the upstream guide vane element to limit leaks of gas flowing in the turbine.
In operation, the hot gases leaving the combustion chamber of the turbomachine flow over the blades of the upstream guide vane element and apply axial pressure to the latter which pushes the upstream guide vane element in the downstream direction. The outer periphery of the upstream guide vane element then tends to press axially on the annular support for coupling the ring sectors and to push it in the downstream direction, which causes random and uncontrolled variations in the radial clearances between the movable blades of the impeller and the ring sectors and therefore reduces the performance of the turbomachine.